1) Field of the Invention
This invention relates generally to liquid spraying devices and particularly to a nozzle that is self cleaning and more particularly to a nozzle that has a vacuum hood which delivers a vacuum to remove residue from the nozzle and exterior of the nozzle.
2) Description of the Prior Art
Great improvements have been made to liquid and aerosol spraying nozzles over the last decade. Nozzles and sprayers have become very complicated, small, and efficient However, in many applications nozzles spray liquids, aerosols, and suspensions of solids, etc., which can leave residues on the tip of the nozzle and on the outside of the nozzle. These liquid and solid residues can clog or partially block the nozzle. Also, these residues can drip from the nozzle onto critical parts thereby damaging the parts. For example, this occurs in the manufacture of semiconductor chips, and especially in the rinsing of photoresist from the top periphery of a wafer.
The problem of nozzles dripping residue and damaging product occurs in the rinsing of photoresist from wafers. A first photoresist layer is coated on a semiconductor wafer. Then in a photoresist rinse operation, the photoresist is rinsed away from the edge of the wafer. The photoresist is removed from the edge of the wafer because it will contaminate the equipment in the next process step. A rinse nozzle sprays thinner onto the edge of the spinning wafer to remove the photoresist from only the edge of the wafer. FIG. 1A shows a side view of a wafer 2 with a photoresist layer 4 covering the top side 6 of the wafer and also overhanging the edge of the wafer. FIG. 1B shows the photoresist layer rinsed off from the sides and top edge of the wafer. For example for a wafer with about a 150 mm diameter, about 2 and 3 mm of the photoresist would be removed from the edge 8. FIG. 1C shows the result of the problem when thinner drips from the nozzle onto a wafer. The photoresist 4 develops patches 5 where the wafers have to be reworked or destroyed. The small nozzle used in the photoresist operation exacerbates the drip problem.
Several methods have been tried to keep the nozzles clean. In U.S. Pat. No. 5,147,087 to Fuchs, after a spray medium is stopped from flowing through a discharge nozzle, a compressed air is flowed to clean out the inside of the nozzle. U.S. Pat. No. 4,093,123 to Maran, teaches a method which cleans out the inside of a paint sprayer by turning the paint spray can upside down, to halt the spray of paint and to flow air through the nozzle. In U.S. Pat. No. 4,832,752 to Nezworski, a nozzle cleaning method is disclosed using cleansing and deliming solution, for a washing machine application.
However, these devices and methods do not adequately solve the problem of nozzle discharge residues forming on the tip and on the outside of the tip. These residues can be liquid, combinations of liquids and solids, and solids. These residues can degrade the function of the nozzle by for example, clogging the nozzle tip or dripping from the outside of the nozzle tip onto some other work. There is a need to develop a nozzle device and method of dispensing fluids from a nozzle which prevents fluids from dripping from the nozzle.